Well, on the contrary...
Revive Adserver processes and stores hardly any personal data.
Either way, Revive Adserver is just a piece of software. The publisher using it is ultimately responsible for how they use it. They are the 'data controller' and most likely also the 'data processor'. Nothing new here, same for any other software being used by the same publisher.
GDPR is not a technical issue, it's primarily a legal issue.
Also, GDPR has been in effect since May 25, 2016. Everyone should have been compliant for a long time already. The only thing new is that enforcement will start on May 25, 2018.

It may be that you ran into an issue that was found in the upgrade process in v4.1.0 and that was fixed in v4.1.1. Please try if using the most recent version fixes this for you. See https://www.revive-adserver.com/download/ and https://www.revive-adserver.com/blog/revive-adserver-v4-1-1-released-bug-fixes/

Technical requirements for Revive Adserver v4.0.x are listed here: https://www.revive-adserver.com/support/requirements/
As you can see, PHP 7.1.x is not yet officially supported. I've opened an issue on Github for the developers to look into this, see https://github.com/revive-adserver/revive-adserver/issues/837

That "dashboard" page isn't extremely useful, and not at all critical to the working of the ad server. I would recommend just disabling it altogether and you won't see that message anymore.
To disable it:
log in as an administrator, and switch to "working as administrator"
go to the Configuration tab, and then "User interface settings" menu item on the left
at the very end of that page, uncheck the "Enable dashboard" checkbox
don't forget to save the changes
Problem solved.

There is no feature to 'save' such settings. All you do is to switch to the desired type of invocation code (in your case javascript) and then generate the tags (again).
Next, you copy the javascript code that the application has generated and you paste it into your target environment.